GB2088486A - Dry powder pump - Google Patents

Abstract

A dry powder pump comprises means (3) defining a powder space, means (10, 11) operative to draw powder into the space from a powder source (4) and to force powder from said space to a delivery point (22, 28), powder fludising means comprising at least one gas pervious area (50 to 58) in the surface of the means defining the powder space, and means to release gas under pressure (open arrows) through those areas into the space in quantity sufficient to fludise the powder and facilitate its movement through the space. <IMAGE>

Description

SPECIFICATION Dry powder pump This invention relates to the mechanised handling, particularly the pumping of dry powders in bulk and is applicable to the movement of dry powders in industrial processes involving such a powder. For example the invention is applicable to the conveying of portland cement powder in a concrete mixing plant.

The conveying of dry powders presents considerable problems by comparison with those arising in relation to other materials. For example, the powder has to be contained at all times to prevent leakage in the same way as a liquid material has to be contained, but, unlike a liquid, dry powder is not readily pumped through pipes because of the very high pressures required to cause it to flow.

Hitherto the mechanised handling of dry powder has been achieved by one or other of the following apparatus.

1. Pneumatic conveyors, in which the powder is entrained in an airstream or the like.

2. Screw conveyers.

3. Bucket conveyors and elevators.

4. The "Flowveyor", which comprises a tube along which a series of discs are hauled by a wire and which function as pistons to force the powder along the tube.

5. The "Fuller Kinyon" Pump, which is an almost airtight screw which propels the dry powder into the path of an air stream within a tube thus avoiding the necessity of pressurising the storage silo or container from which the powder is drawn.

All forms of pneumatic entrainment conveying have one drawback in that they use a lot of air and therefore require a lot of power. Furthermore after delivery the powder must be separated from the air, which process requires expensive equipment to avoid atmospheric pollution.

On the other hand the previous known alternatives lack flexibility in operation and are prone to spillage.

According to the present invention a dry powder is moved by fluidising the powder and pumping the fluidised powder. This overcomes the disadvantages of prior known techniques: the powder is simply aerated sufficiently to fluidise it and then pumped as if it were a liquid. It will be appreciated that the quantity of gas needed to fluidise the powder is far less than that required to entrain the powder in a gas stream. Furthermore it has been found that fluidised powder may be readily pumped to a high pressure for delivery through pipes to a remote situation.

In preferred versions of the invention the fluidising gas is air and is admitted or admixed with the powder in the pump itselt.

Thus the invention provides a dry powder pump comprising means defining a powder space, means to draw powder into the space from a powder source and to force powder from the space to a delivery point, and powderfluidising means comprising at least one gas pervious area in the surface of the means defining the powder space and means to release gas under pressure through that area into the space in quantity sufficient to fluidisethe powder and facilitate its movement through the space.

For preference the pump, apart from the fiuidising means, may be a simple force pump that is to say a pump comprising a cylinder, a piston reciprocating in the cylinder and inlet and outlet valves permitting material to flow into the cylinder during the return stroke of the piston and permitting material to flow out of the cylinder during the forward or power stroke of the piston.

By way of example, an embodiment of the invention is described in more detail hereinafter with reference to the accompanying drawings, in which: Figure 1 is a sectional view of a double acting force pump according to the invention, Figure 2 is a sectional view of the piston and piston rod assembly of the pump of Figure 1 drawn to a larger scale, and, Figure 3 is a diagram of an hydraulic system for operating the pump.

The pump illustrated comprises a body 3, an inlet port 4, outlet ports 5 and 6, an inlet valve 7, outlet valves 8 and 9, a piston and piston rod assembly 10 and a double acting hydraulic thrustor 11 connected to the piston and rod assembly 10 by way of a cross head 12 to effect reciprocation of the assembly 10.

The body 3 is a plain, open-ended cylinder but for a spigot 13 projecting from it midway of its ends. The spigot 13 constitutes a portion of the inlet port 4.

The inlet valve 7 is a butterfly valve and comprises an annular valve body 14, a cranked spindle 15 extending diametrically of the body 14, a valve vane 16 fixed to the spindle 15 and a double acting hydraulic thrustor 17 connected to the cranked end of the spindle 15 and able to rotate the spindle through 90 so as to open or close the valve as the case may be.

The inlet duct 4 also comprises a flanged, tubular pipe connector 18 adapted to be bolted to the outlet of an inverted conical, powder supply hopper 19.

The valve body 14 is sandwiched between the connector 18 and spigot 13 and the entire inlet port4 comprising the spigot 13, valve body 14 and connector 18 is maintained as a unitary structure by tie bolts 20.

Outlet port 5 comprises a pipe bend 21, a tapered, flanged, pipe connector 22 and a valve body 23, being the body of the outlet valve 8.

The components of the outlet duct 5 are held together by tie bolts 27 in the same manner as the components of the inlet duct 4.

The outlet valve 8 comprises the body 23, a cranked spindle 24, a butterfly vane 25, and a double acting thruster 26 The outlet duct 6 is similar to duct 5 and comprises a pipe bend27, a valve body 78, being the body of inlet butterfly valve 6, a tapered pipe connector 28 and tie bolts 29.

The outlet ducts 5 and 6 are secured to the body 3 to form a unitary construction by means of further tie bolts 30.

The spindle of valve 9 is linked (by means not shown) to the spindle 24 of valve 8 so that valves 8 and 9 operate in concert with one valve opening as the other valve closes. In relation to those valves and the inletvalve 7 itwill be appreciatedthatthe operating mechanism and indeed the valves themselves as seen in Figure 1 are illustrated in a diagrammatic manner.

The body 3 and the outlet ducts 5 and 6 are mounted upon a fabricated steel chassis 31 to which the thrustor 17 is pivotally secured at one end.

The thrustor 11 is a conventional double-acting hydraulic cylinder and piston typethrustor in which the piston moves to and fro to cause the piston rod to reciprocate by forward and return strokes. The thrustor's piston rod is pivotally connected to the cross head 12 and the latter is slidable on a guide rod 32 fixedly mounted on the chassis 31. The cross head 12 is also pivotally connected at33 to a tubular piston rod 34 being a component of the piston and piston rod assembly 10. The tubular rod 34 is slidable through a gland 35 extending through the outer curved wall of the pipe bend 27. The gland 35 is conventional in nature and has a tubular gland nut 36 which compresses packing material 37 against the tubular rod 34to seal the gland against leakage.

For preference, the gland is lubricated by means of a lubricating nipple and duct arrangement 38. Also, it may be rendered less prone to leakage by means of pressurizing duct 39 adapted to receive air from a pressurized source. It is believed that to those skilled in the art, the general construction and function of the gland 35 will be well understood from the foregoing brief description.

The piston rod 34 carries a piston 40, which will be described in more detail hereinafter.

In use the piston 40 may be caused to reciprocate and the inlet and outlet valves cause to open and close in synchronism with the reciprocation of the piston 40 to produce a pumping action.

An hydraulic system whereby such concerted operation of the piston and valves may be effected, is indicated in figure 3 wherein 42 is a hydraulic fluid sump, and 43 is a pump which draws fluid from the sump 42 and distributes itto the remainder of the hydraulic system.

The output pressure from the pump 43 is controlled by a pressure relief valve 44.

The full pressure of the pump 43 is delivered to a change-oversolenoid operated valve 45 controlling the operation of the thrustor 11.

The output pressure from the pump 43 is reduced by way of a pressure'reducing valve 46 and then fed to further solenoid operated change-over valves 47 and 48 controlling the operations of thrustors 26 and 17 respectively.

The valves 45,47 and 48 may be operated from an electric supply by way of limit switches (not shown) co-operating with the piston rod 34 or one or other of the components which reciprocate with it Insofar as it has been described above the pump and control apparatus are substantially conventional in nature and it is thought that a more detailed description will not be required by a person skilled in the art.

In accordance with the present invention, powder fluidising means are provided for liberating air into the powder being pumped in quantities sufficient to fluidize the powder so that it may be pumped as if, or substantially as if, itwere a liquid. It should be emphasised that the quantity of air liberated into the powder is very much less than would be needed for the entrainment of the powder in an air stream, it being the mechanical pumping action of the piston 40 which effects the movement of the powder through the pump.

The powder fluidising means generally comprise a jacket covering a portion of the surface of a component defining the powder space within the pump and an opening or perforations in that component enabling air supplied to the jacket to be released into the powder space. For preference, the inflow of air is effected through a porous diaphragm such as, for example, a woven fabric or the like.

Thus the pipe bend 21 has powder fluidising means covering part of its outer surface comprising a jacket 49, a plurality of perforations 50, a woven fabric sheet 51 and a spigot 52 through which air from a pressurized source (not shown) may be fed to the space between the jacket and the bend for liberation into the powderthrough the fabric sheet 51 and the perforations 50.

Likewise the pipe connector 22 may be encircled by a jacket 53 and a woven fabric sleeve 54 covering four relatively large openings 55 in the curved walls of the connector.

The pipe connector 28 may be furnished with fluidizing air delivery means 56 the same as those just described in relation to the connector 22.

Then again, at 57t pipe bend 27 may be furnished with such means essentially the same as those described in relation to pipe bend 21. In this case the air admission means 57 are somewhat smaller than the corresponding means of bend 21 because of the intrusion of the gland 35, therefore additional air admission means may be provided at 58 comprising a small jacket 69 and pervious fabric 51 covering a relatively large opening in the wall of bend 27.

Of particular importance is the liberation of air through the piston 40 to the powder mass in contact with it To that end the powder fluidising means associated with the assembly 10 may be furnished, comprising an innertube 59 coaxial with and extending through the tubular piston rod 34. Air under pressure is supplied from an appropriate source to nipples 60 and 61 for infeed into the annular space between rod 34 and tube 59 on the one hand and the interior of tube 59 on the other, for escape into the powder from piston 40. The connection to the nipples 60 and 61 may be by way of flexible air supply - hoses so as not to interfere with the reciprocation of the assembly 10.

The piston 40 comprises two spaced apart discs 62 and 63 respectively and two woven fabric membranes 64 and 65. Air from tube 59 is fed to one side of disc 62 for escape through the membrane 64 whereas air from the annular space between tube 59 and rod 34 flows by way of perforations 66 in the disc 63 to and then through the membrane 65.

In all cases the air is preferably provided from a pressurized source at a pressure which is at least equal to and preferably somewhat in excess of the maximum pressure applied to the fluidized powder duringthe pumping operation. Likewise, it may be air from that source which is supplied to the nipple and duct 39.

For preference, the air supply to the diaphragms 64 and 65 and to the respective outlet ducts 5 and 6 is separately controlled. In that event it may be switched on and off two provide for air pressure within the cylinder ahead of the piston during the compression or power stroke of the piston towards one or other outlet port and for a reduction in air pressure behind the piston. This facilitates the drawing-in of powder through the inlet port. Underthose circumstances and indeed even if the air pressure is maintained constant there is a pressure differential across the piston and that differential would result in leakage of powder across the piston as the piston comes into alignment with the inlet duct 4. To prevent such leakage the piston preferably has a part cylindrical shield 67 secured to it which ensures that the duct4 is closed for so long as the piston is in alignment with its bore.

Because, apart from thefluidizing air supply means the pump may be conventional itwill be appreciated that the invention may be applied to types of pump other than that illustrated in the drawings. In particular it may be applied to single acting force pumps, centrifugal pumps or practically any known type of pump.

Claims (7)

1. A dry powder pump comprising means defining a powder space, means to draw powder into the space from a powder source and to force powder from the space to a delivery point, and powder fluidising means comprising at least one gas pervious area in the surface of the means defining the powder space and means to release gas under pressure through that area into the space in quantity sufficient to fluidise the powder and facilitate its movementthrough the space.

2. A pump according to claim 1 wherein the gas pervious area comprises at least one opening in the surface and a gas pervious membrane covering that opening.

3. A pump according to claim 2 wherein the membrane is a woven fabric membrane.

4. A pump according to any one of the preceding claims wherein the means to release gas under pressure comprise a jacket covering the area and means to deliver gas under pressure into the interior of the jacket.

5. A pump according to any one of claims 1 to 4 and comprising a cylinder, a piston reciprocating in the cylinder and inlet and outlet valves permitting material to flow into the cylinder during the return stroke of the piston and permitting material to flow out of the cylinder during the forward or power stroke of the piston.

6. A method of moving a dry powder comprising the steps of fluidising the powder and then pumping the fluidised powder.

7. A dry powder pump substantially as described herein with reference to the accompanying drawings.